This magic trick is caused by the light refracting through the glass of water. The glass of water acts as a convex lens, as it refracts the arrow, the image becomes inverted, so the arrow looks like it is facing the other way. The image also looks like it’s bent because the index of refraction in the water is greater than the air, which changes the speed of the light therefore bending the light.
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This video demonstrates a periodic wave, this wave is recurring at regular intervals.
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This video demonstrates a pulse wave, this is a non-repeating wave.
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This video demonstrates a transverse wave, this is when the spring is pulled sideways.
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This video demonstrates a longitudinal wave, it is compressed and then released, forming a wave.
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This video demonstrates constructive interference, here two crest waves (could also be two trough waves) collide to make one wave who’s size is the sum of the previous waves, and then it separates back into the two waves and they continue in the same direction.
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This video demonstrates destructive interference, here a crest and a trough collide, when they collide they cancel out, but then turn back to their original waves and continue moving.
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This video demonstrates standings waves. The waves have the same amplitude and and wavelength, as a result the waves look stationary and five nodes are formed.